Ultraviolet curable silver composition and related method

ABSTRACT

A photocurable silver composition is provided which comprises an ultraviolet light curable organic mixture, a photoinitiator, a silver powder, and a silver flake composition. The silver flake composition comprises at least 20% of the weight of the silver powder. The disclosed compositions may be used to produce silver-containing coatings on a variety of different substrates. Related methods are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.09/413,577 filed on Oct. 6, 1999 now U.S. Pat. No. 6,290,881 which is acontinuation-in-part of U.S. application Ser. No. 09/291,774, filed Apr.14, 1999 now abandoned.

TECHNICAL FIELD

The present invention relates to silver-containing compositions and moreparticularly to photocurable silver-containing compositions, to methodsfor making and applying a photocurable silver-containing compositions asa coating on a substrate.

BACKGROUND ART

There are many instances in which it is necessary or desirable to applya coating, plating or layer of silver or a silver-containing compound toa substrate. Examples of such applications would include electrodeplating for switches such as those used on pressure-sensitive switchesor control panels, for example, as are used on appliances such asmicrowave ovens, conventional ovens, and the like. Such silver platingalso is commonly used in the semiconductor fabrication arts to applysilver metalizations on silicon or germanium semiconductor wafers. Otherexamples of such substrates include, without limitation, such things aspolyesters, polycarbonates, vinyls, ceramics, glass, and the like.

The predominant approach heretofore used in applying silver tosubstrates has involved using a solvent-based silver solution to thesubstrate, and chemically or thermally curing the solution to evaporatethe solvent. This leaves the solid silver plating on the substrate.

This conventional approach is disadvantageous in a number of respects.Of perhaps the greatest concern is the fact that the solvents currentlyused for this purpose are toxic. They require special handling anddisposal facilities and techniques, and correspondingly increaseinefficiencies and costs. Even while observing these special handlingtechniques, they present hazards to workers using these toxic materials.The solvent-based compositions and methods also are disadvantageous inthat it can be difficult to predict the uniformity and thickness of theresultant silver plating after the solvent has evaporated. This leads toquality and performance variations.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a silvercomposition and method in which silver can be disposed on a substratewithout requiring a toxic solvent.

Another object of the invention is to provide a silver composition andmethod in which disposition of the silver layer can be done more quicklyand efficiently than prior art solvent-based techniques.

Another object of the invention is to provide a silver composition andmethod in which a silver coating may be created which has morepredictable and uniform layer thickness relative to prior artsolvent-based systems.

To achieve the foregoing objects, and in accordance with the purposes ofthe invention as embodied and broadly described in this document, asilver composition is provided for deposition as a coating, plating,film or layer on a substrate. The terms coating, plating, film and layerin the context of this document are used to refer generally to acovering on the surface of a substrate, which covering may be of avariety of thicknesses depending on the application and the designgoals.

DISCLOSURE OF INVENTION

In accordance with one aspect of the invention, a photocurable silvercomposition is provided. The silver composition comprises a photocurableorganic mixture, a photoinitiator, a silver powder, and a silver flakecomposition. The silver flake composition is present in an amount of atleast 20% of the weight of the silver powder present in the composition.Incorporation of silver flake composition in an amount of at least 20%results in films with superior conductivity. Resistivities as low as0.03 ohm/sq at 1 mil are achieved.

The photocurable silver composition preferably comprises an aliphaticacrylated oligomer, wherein the aliphatic acrylated oligomer is presentin an amount of about 3% to 8% based on the weight of the silvercomposition. All percentages of the silver composition as expressed inthis document, unless otherwise stated, refer to the mass percentage ofthe stated component to the total mass of the silver composition in itsfluid uncured state at standard temperature and pressure.

The silver composition also preferably comprises an acrylated epoxyoligomer, wherein the acrylated epoxy oligomer is present in an amountof about 2% to 4% of the silver composition.

The silver composition also preferably comprises an isobornyl acrylatemonomer in an amount of about 4% to 8% of the silver composition, aphotoinitiator in an amount of about 3% to 6% of the silver composition,a flow promoting agent in an amount of about 0.1% to 2% of the silvercomposition, a silver powder in an amount of about 50% to 60% of thesilver composition, and a silver flake composition in an amount of about25% to 35% of the silver composition.

In accordance with this aspect of the invention, the aliphatic acrylatedoligomer preferably comprises a urethane oligomer. In presentlypreferred versions of the silver composition, the aliphatic acrylatedoligomer is present in an amount of about 8% of the silver composition.

The acrylated epoxy oligomer is preferably present in an amount of about3% of the silver composition. The isobornyl acrylate monomer ispreferably present in an amount of about 5% of the silver composition.The photoinitiator is preferably present in an amount of about 5% of thesilver composition. The flow promoting agent is preferably present in anamount of about 1% of the silver composition.

In presently preferred embodiments according to this aspect of theinvention, the silver powder preferably but optionally is present in anamount of about 52% of the silver composition. In these preferredembodiments, the silver powder has a particle size range of about 5microns to about 15 microns. In a more preferred embodiment, the silverpowder has a particle distribution such that about 5% to 20% of theparticles have a particle size of less than about 4.7 microns, about 30%to 60% of the particles have a particle size of less than about 7.6microns, and about 70% to 95% of the particles have a particle size ofless than about 14.9 microns. In the most preferred embodiment, thesilver powder has a particle distribution such that about 10% of theparticles have a particle size of less than about 4.7 microns, about 50%of the particles have a particle size of less than about 7.6 microns,and about 90% of the particles have a particle size of less than about14.9 microns.

According to the presently preferred embodiments, the silver flake ispresent in an amount of about 30% of the silver composition. Preferablythe silver flake has a particle size range of about 5 microns to about32 microns. The silver flake preferably has a flake distribution suchthat about 10% of the particles have a particle size of less than about5.5 microns, about 50% of the particles have a particle size of lessthan about 12.5 microns, and about 90% of the particles have a particlesize of less than about 32.0 microns.

In a further refinement of the presently preferred embodiment, anadhesion promoter is present in about 1 to 4% of the silver composition.This further refinement improves adhesion to substrates coated withtransparent conductors such as indium tin oxide (ITO).

In accordance with another aspect of the invention, a photocurablesilver composition suitable for producing a coating that is capable ofshielding electromagnetic radiation is provided. This embodiment ispreferably applied to a substrate by spraying. The silver compositioncomprises an acrylated epoxy oligomer, wherein the acrylated epoxyoligomer is present in an amount of about 2% to 8% of the silvercomposition. The silver composition preferably comprises an isobornylacrylate monomer in an amount of about 15% to 30% of the silvercomposition, an photoinitiator in an amount of about 3% to 7% of thesilver composition, a flow promoting agent in an amount of about 0.1% to2% of the silver composition, a silver powder in an amount of about 20%to 40% of the silver composition, and a silver flake composition in anamount of about 20% to 40% of the silver composition.

In accordance with another aspect of the invention, a photocurablesilver composition suitable for producing a coating that is capable offorming resistive links on circuit boards is provided. This embodimentof the invention preferably does not contain any urethane The silvercomposition comprises an acrylated epoxy oligomer having, wherein theacrylated epoxy oligomer is present in an amount of about 16% to 20% ofthe silver composition. The silver composition also comprises anisobornyl acrylate monomer in an amount of about 8% to 14% of the silvercomposition, an photoinitiator in an amount of about 4% to 8% of thesilver composition, a flow promoting agent in an amount of about 0.1% to2% of the silver composition, a silver powder in an amount of about 25%to 38% of the silver composition, and a silver flake composition in anamount of about 20% to 40% of the silver composition.

In accordance with yet another aspect of the invention, a photocurablesilver composition suitable for producing a coating that is capableresistive links on circuit boards is provided. This embodiment containsurethane. The silver composition comprises an aliphatic acrylatedoligomer (a urethane), wherein the aliphatic acrylated oligomer ispresent in an amount of about 7% to 11% of the silver composition. Thesilver composition further comprises an acrylated epoxy oligomer,wherein the acrylated epoxy oligomer is present in an amount of about 1%to 4% of the silver composition. The silver composition also comprisesan isobornyl acrylate monomer in an amount of about 12% to 25% of thesilver composition, a photoinitiator in an amount of about 2% to 4% ofthe silver composition, a flow promoting agent in an amount of about0.0% to 4% of the silver composition, an antimony tin oxide powder in anamount of 7% to 19%, a silver powder in an amount of about 24% to 30% ofthe silver composition, and a silver flake composition in an amount ofabout 15% to 30% of the silver composition. In a further refinement ofthis embodiment, the silver composition further comprises a polyacrylicoligomer/acrylate monomer blend in an amount of about 5% to 10%.

In accordance with yet another aspect of the invention, a photocurablesilver composition suitable for producing a coating that is capableblack colored resistive links on circuit boards is provided. The silvercomposition comprises an aliphatic acrylated oligomer, wherein thealiphatic acrylated oligomer is present in an amount of about 7% to 11%of the silver composition The silver composition further comprises anacrylated epoxy oligomer having, wherein the acrylated epoxy oligomer ispresent in an amount of about 2% to 4% of the silver composition. Thesilver composition also comprises an isobornyl acrylate monomer in anamount of about 10% to 14% of the silver composition, a photoinitiatorin an amount of about 13% to 15% of the silver composition, a flowpromoting agent in an amount of about 0.1% to 2% of the silvercomposition, a conductive carbon black powder in an amount of 5% to 12%,a wetting agent in an amount of about 0.5 to 3% of the silvercomposition, a silver powder in an amount of about 30% to 40% of thesilver composition, and a silver flake composition in an amount of about15% to 25% of the silver composition.

In accordance with another aspect of the invention, a method is providedfor making a photocurable silver composition. The method comprises afirst step of combining and mixing an isobornyl acrylate monomer and aphotoinitiator to create a first mixture. The isobornyl acrylate monomeris present in an amount of about 4% to 8% of the silver composition, andthe photoinitiator is present in an amount of about 3% to 6% of thesilver composition.

The method includes a second step of combining and mixing an aliphaticacrylated oligomer and an acrylated epoxy oligomer to create a secondmixture. The aliphatic acrylated oligomer is present in an amount ofabout 3% to 8% of the silver composition and the acrylated epoxyoligomer is present in an amount of about 2% to 4% of the silvercomposition.

The method includes a third step of combining and mixing a silver powderand a silver flake composition to create a third mixture. The silverpowder is present in an amount of about 50% to 60% of the silvercomposition and the silver flake composition is present in an amount ofabout 25% to 35% of the silver composition.

The method further includes a fourth step of combining and mixing a flowpromoting agent in an amount of about 0.1% to 2% of the silvercomposition, and a fifth step of combining the first, second, third andfourth mixtures to create the silver composition.

Preferably, but optionally, the first, second, third and fourth stepsare performed sequentially. The method in its various forms may becarried out on a batch basis, for example, in a mixing vessel or similarprocess equipment suitable for batch processing. It may also be carriedout in other forms, for example, such as continuous flow regimes.

In accordance with another aspect of the invention, another method isprovided for making a photocurable silver composition. This methodcomprises a first step of combining and mixing an isobornyl acrylatemonomer and a photoinitiator to create a first composition, wherein theisobornyl acrylate monomer is present in an amount of about 4% to 8% ofthe silver composition, and the photoinitiator is present in an amountof about 3% to 6% of the silver composition. This method also includes asecond step of combining with the first composition and mixing analiphatic acrylated oligomer and an acrylated epoxy oligomer to create asecond mixture. The aliphatic acrylated oligomer is present in an amountof about 3% to 8% of the silver composition and the acrylated epoxyoligomer is present in an amount of about 2% to 4% of the silvercomposition.

The method further includes a third step of combining with the secondcomposition and mixing a silver powder and a silver flake composition tocreate a third composition. The silver powder is present in an amount ofabout 50% to 60% of the silver composition and the silver flakecomposition is present in an amount of about 25% to 35% of the silvercomposition.

The method still further includes a fourth step of combining with thethird composition and mixing a flow promoting agent in an amount ofabout 0.1% to 2% of the silver composition.

This method also may be carried out in a batch format, for example, in amixing vessel or series of mixing vessels, in a continuous flow regime,or in some combination.

In accordance with yet another aspect of the invention a method isprovided for depositing a silver coating on a substrate. The methodcomprises a first step of applying to the substrate a silver-containingfluid-phase composition (“silver composition”). The silver compositioncomprises an aliphatic acrylated oligomer, wherein the aliphaticacrylated oligomer is present in an amount of about 3% to 8% of thesilver composition. The silver composition further includes an acrylatedepoxy oligomer. The acrylated epoxy oligomer is present in an amount ofabout 2% to 4% of the silver composition. The silver composition alsoincludes an isobornyl acrylate monomer in an amount of about 4% to 8% ofthe silver composition, a photoinitiator in an amount of about 3% to 6%of the silver composition, and a flow promoting agent in an amount ofabout 0.1% to 2% of the silver composition. The silver compositionfurther includes a silver powder in an amount of about 50% to 60% of thesilver composition, and a silver flake composition in an amount of about25% to 35% of the silver composition.

The method also includes a second step of illuminating the silvercomposition on the substrate with light of a wavelength suitable tocause the silver composition to cure into the silver coating. Preferablylight will have a wavelength in the ultraviolet region of theelectromagnetic spectrum.

In accordance with this method, the silver composition can beselectively deposited on the substrate at specific locations wheresilver plating is desired. It need not be applied to the entiresubstrate. It is thus possible, for example, to use the silver coatingthus created as metalizations on semiconductor wafers, printed circuitboards, pressure sensitive or pressure activated switches, and the like.

According to another aspect of the invention, a method is provided forpreparing a liquid-phase silver-containing composition for use inproviding a silver-containing coating or plating on a substrate. Thepresently preferred version of the method includes preparing thecomposition as identified immediately above. The method in broad termsincludes a first step of combining and mixing the monomer and thephotoinitiator in a mixing vessel, a second step of adding to the mixingvessel and blending in the urethane and the epoxy, a third step ofadding to the mixing vessel and blending in the silver powder and thesilver flake, and a forth step of adding to the mixing vessel andblending in the flow agent.

BEST MODE FOR CARRYING OUT THE INVENTION

Silver Compositions

Reference will now be made in detail to presently preferred compositionsor embodiments and methods of the invention, which constitute the bestmodes of practicing the invention presently known to the inventor.

In accordance with one aspect of the invention, a presently preferredphotocurable silver composition (“silver composition”) is provided. Inthis preferred embodiment, the silver composition includes an aliphaticacrylated oligomer. The aliphatic acrylated oligomer is present in anamount of about 3% to 8%, and preferably about 8%, of the silvercomposition. The aliphatic acrylated oligomer preferably comprises aurethane oligomer. Suitable aliphatic acrylated oligomers includeRadcure Ebecryl 244, Ebecryl 264 and Ebecryl 284 urethanes, commerciallyavailable from Radcure UCB Corp. of Smyrna, Ga.; Sartomer CN961, CN963,CN964, CN 966, CN982 and CN 983, commercially available from SartomerCorp. of Exton, Pa.; TAB FAIRAD 8010, 8179, 8205, 8210, 8216, 8264,M-E-15, UVU-316, commercially available from TAB Chemicals of Chicago,Ill.; and Echo Resin ALU-303, commercially available from Echo Resins ofVersaille, Mo.; and Genomer 4652, commercially available from RahnRadiation Curing of Aurora, Ill. The preferred aliphatic acrylatedoligomers include Ebecryl 264 and Ebecryl 284. Ebecryl 264 is analiphatic urethane triacrylate supplied as an 85% solution in hexandioldiacrylate. Ebecryl 284 is aliphatic urethane diacrylate of 1200molecular weight diluted with 1,6-hexandiol diacrylate. It is obvious toone skilled in the art that combinations of these materials may also beemployed herein.

This preferred silver composition further includes an acrylated epoxyoligomer. The acrylated epoxy oligomer is present in an amount of about2% to 4%, and preferably about 3%, of the silver composition. Suitableacrylated epoxy oligomers include Radcure Ebecryl 3603, commerciallyavailable from Radcure UCB Corp.; Sartomer CN120 and CN124, commerciallyavailable from Sartomer Corp.; and Echo Resin TME 9310 and 9345,commercially available from Echo Resins. The preferred acrylated epoxyoligomer is Ebecryl 3603, which tri-functional acrylated epoxy novolac.Combinations of these materials may also be employed herein.

The preferred silver composition also includes an isobornyl acrylatemonomer in an amount of about 4% to 8%, and preferably about 5%, of thesilver composition. Suitable isobornyl acrylate monomers includeSartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA and IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing. Preferred isobornyl acrylate monomers include SartomerSR423 IBOMA and SR506 IBOA; Radcure IBOA, commercially available fromRadcure Corp.; IBOA AND IBOMA, commercially available from CPS Chemical;and Genomer 1121, commercially available from Rahn Radiation Curing.

This preferred silver composition also includes a photoinitiator in anamount of about 3% to 6%, and preferably about 4%, of the silvercomposition. Suitable photoinitiators include Irgacure 184(1-hydroxycyclohexyl phenyl ketone), 907(2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one), 369(2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone), 500(the combination of 1-hydroxy cyclohexyl phenyl ketone andbenzophenone), 651 (2,2-dimethoxy-2-phenyl acetophenone), 1700 (thecombination of bis(2,6-dimethoxybenzoyl-2,4-,4-trimethyl pentylphosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one),Ciba-Geigy 1700, and DAROCUR 1173 (2-hydroxy-2-methyl-1phenyl-1-propane)and 4265 (the combination of 2,4,6-trimethylbenzoyldiphenyl-phosphineoxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one), availablecommercially from Ciba-Geigy Corp., Tarrytown, N.Y.; CYRACURE UVI-6974(mixed triaryl sulfonium hexafluoroantimonate salts) and UVI-6990 (mixedtriaryl sulfonium hexafluorophosphate salts) available commercially fromUnion Carbide Chemicals and Plastics Co. Inc., Danbury, Conn.; andGenocure CQ, Genocure BOK, and GenocureMBF, commercially available fromRahn Radiation Curing. The preferred photoinitiator is Irgacure 1700commercially available from Ciba-Geigy of Tarrytown, N.Y.

The preferred silver composition still further includes a flow promotingagent in an amount of about 0.1% to 2%, and preferably about 1.0%, ofthe silver composition. Suitable flow promoting agents include Genorad17, commercially available from Rahn Radiation Curing; and Modaflow,commercially available from Monsanto Chemical Co., St. Louis, Mo. Thepreferred flow promoting agent is Modaflow which is an ethyl acrylateand 2-ethylhexyl acrylate copolymer that improves the flow of thecomposition. Combinations of these materials may also be employedherein.

The preferred silver composition also includes a silver powder in anamount of about 50% to 60%, and preferably about 52%, of the silvercomposition. The silver powder comprises a plurality of particles. Inthis preferred silver composition, the silver powder has a particle sizerange for these particles of about 5 microns to about 15 microns. Insome embodiments, the silver powder has a particle size range of about4.7 microns to about 14.9 microns. Preferably, the silver powderparticles have a particle size distribution wherein about 10% of theparticles have a particle size of less than about 4.7 microns, about 50%of the particles have a particle size of less than about 7.6 microns,and about 90% of the particles have a particle size of less than about14.9 microns. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

The preferred silver composition further includes a silver flakecomposition in an amount of about 25% to 35%, and preferably about 30%,of the silver composition. The silver flake composition comprises aplurality of flakes which comprise, and which preferably consistessentially of, silver. The silver flake composition according to thisembodiment has a particle size range of about 5 microns to about 32microns. More preferably, the silver flake composition has a particlesize range of about 5.5 microns to about 32.0 microns. The silver flakeparticle size distribution preferably is such that about 10% of theparticles have a particle size of less than about 5.5 microns, about 50%of the particles have a particle size of less than about 12.5 microns,and about 90% of the particles have a particle size of less than about32.0 microns. The preferred silver flake compositions are Silver Flake#25, Silver Flake #1, and Silver Flake #7A commercially available fromDegussa Corp. of South Plainfield, N.J.

EXAMPLE 1

This example provides a preferred silver composition according to theinvention that can be used for deposition on the surface of a substratesuch as a polymeric membrane, for example, to serve as the electricalcontact for a pressure-sensitive switch. The silver composition was madefrom the following components:

Component Approximate Mass % Ebecryl 264 7.2 Ebecryl 3603 2.4 IBOA 4.7Silver Powder EGED 53.4  Silver Flake # 25 27.6  Iragure 1700 3.9Modaflow 0.8 Total 100.00 

In this example the IBOA and Iragure 1700 are mixed in a pan with apropeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the EGED silver powder, and the Silver Flake #25 areintroduced into the pan and are mixed for 1 to 2 minutes at a speed of1000 rpm. Finally, the mixing speed is increased to 10,000 rpm and mixedfor an additional 5 minutes.

For best results, the silver powder is washed prior to addition to themixture. The washing process includes a first step of loading the powderin a sealable container. A mixture consisting of 17% methyl ethyl ketoneand 83% silver composition is added to the container and the slurry ismixed with a propeller blade for 5 minutes at 500 rpm. The methyl ethylketone is poured off and the silver powder is allowed to air dry. Duringthe drying stage the powder is periodically mixed.

The silver powder according to the presently-preferred compositioncomprises EGED, commercially available from Degussa Corp. of SouthPlainfield, N.J. Such silver also may be obtained from other commercialsources, e.g., such as Englehard Chemical Co. of Iselin, N.J. Thepresently preferred silver powder has a grain size distribution rangingfrom about 5 microns to about 15 microns. This presently preferredsilver powder has a particle size distribution as follows:

TABLE 1 Silver Powder Particle Size Distribution Size Range (microns)Percentage <4.7 10% <7.6 50% <14.9  90%

As this table indicates, within a sample of the silver powder, 10% ofthe grains have a size of less than 4.7 microns, 50% of the grains havea particle size of less than 7.6 microns, and 90% of the grains have aparticle size of less than 14.9 microns.

The silver flake according to the presently-preferred composition ofExample I comprises SF25, commercially available from Degussa. Thissilver flake composition preferably has a grain size distributionranging from about 5 microns to about 32 microns. It has a particle sizedistribution as follows:

TABLE 2 Silver Flake Composition Particle Size Distribution Size Range(microns) Percentage  <5.5 10% <12.5 50% <32.0 90%

As indicated in Table 2, within a sample of the silver flake, 10% of theflakes have a size of less than 5.5 microns, 50% of the flakes have aparticle size of less than 12.5 microns, and 90% of the flakes have aparticle size of less than 32.0 microns.

EXAMPLE 2

This example provides another preferred silver composition according tothe invention that can be used for deposition on the surface of asubstrate such as those noted above. The silver composition was madefrom the following components:

Component Approximate Mass % Ebecryl 264 4.2 Ebecryl 3603 2.7 IBOA 7.7Silver Powder EGED 53.4  Silver Flake #25 27.6  Iragure 1700 3.8Modaflow 0.6 Total 100.00 

In this example the IBOA and Iragure 1700 are mixed in a pan with apropeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the EGED silver powder, and the Silver Flake #25 areintroduced into the pan and are mixed for 1 to 2 minutes at a speed of1000 rpm. Finally, the mixing speed is increased to 10,000 rpm and mixedfor an additional 5 minutes.

EXAMPLE 3

This example provides another preferred silver composition according tothe invention that can be used for deposition on the surface of asubstrate coated with indium tin oxide (ITO). The silver composition wasmade from the following components:

Component Approximate Mass % Ebecryl 264 7.0 Ebecryl 3603 2.3 IBOA 4.6Silver Powder EGED 52.3  Silver Flake # 25 27.0  Iragure 1700 3.8Modaflow 0.8 Ebecryl 168 2.2 Total 100.00 

In this example the IBOA and Iragure 1700 are mixed in a pan with apropeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the EGED silver powder, and the Silver Flake #25 areintroduced into the pan and are mixed for 1 to 2 minutes at a speed of1000 rpm. In the next step, the Ebecryl 168 is added into the pan andthe combination mixed at 1000 rpm for 1 to 2 minutes. Finally, themixing speed is increased to 10,000 rpm and mixed for an additional 5minutes.

This example contains Ebecryl 168 added as an adhesion promoter. Thismaterial is a methacrylate ester derivative commercially available fromRadcure UCB Corp. of Smyrna, Ga.

Silver Composition for Producing a Coating Capable Of ShieldingElectromagnetic Interference

In accordance with another aspect of the invention, a presentlypreferred photocurable silver composition (“silver composition”) isprovided. This composition upon photocuring produces a coating capableof shielding electromagnet interference. Such a coating may be appliedto substrates requiring shielding from electromagnetic interferencessuch as the interior of radio casings. In this preferred embodiment, thesilver composition includes an acrylated epoxy oligomer. The acrylatedepoxy oligomer is present in an amount of about 2% to 8%, and preferablyabout 5%, of the silver composition. Suitable acrylated epoxy oligomersare the same as listed above. The preferred acrylated epoxy oligomer isEbecryl 3603, which tri-functional acrylated epoxy novolac. Combinationsof these materials may also be employed herein.

The preferred silver composition also includes an isobornyl acrylatemonomer in an amount of about 15% to 30%, and preferably about 21%, ofthe silver composition. Suitable isobornyl acrylate monomers are thesame as listed above. Preferred isobornyl acrylate monomers includeSartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA and IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing. Combinations of these materials may also be employedherein.

This preferred silver composition also includes a photoinitiator in anamount of about 3% to 7%, and preferably about 5%, of the silvercomposition. Suitable photoinitiators are the same as listed above. Thepreferred photoinitiator is Irgacure 1700 commercially available fromCiba-Geigy of Tarrytown, N.Y. Combinations of these materials may alsobe employed herein.

The preferred silver composition still further includes a flow promotingagent in an amount of about 0.1% to 2%, and preferably about 1.0%, ofthe silver composition. Suitable flow promoting agents are the same aslisted above. The preferred flow promoting agent is Modaflow which is anethyl acrylate and 2-ethylhexyl acrylate copolymer that improves theflow of the composition. Combinations of these materials may also beemployed herein.

The preferred silver composition also includes a silver powder in anamount of about 25% to 40%, and preferably about 36%, of the silvercomposition. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

The preferred silver composition further includes a silver flakecomposition in an amount of about 20% to 40%, and preferably about 30%,of the silver composition. The preferred silver flake compositions areSilver Flake #25, Silver Flake #1, and Silver Flake #7A commerciallyavailable from Degussa Corp. of South Plainfield, N.J.

EXAMPLE 4

This example provides another preferred silver composition according tothe invention that when applied to a surface and subsequently cured byultraviolet radiation will produce a coating suitable for shieldingelectromagnetic interference. The silver composition was made from thefollowing components:

Component Approximate Mass % Ebecryl 3603 5.3 IBOA 21.0  Silver PowderEGED 31.5  Silver Flake # 1 35.7  Iragure 1700 5.3 Modaflow 1.2 Total100.00 

In this example the IBOA and Iragure 1700 are mixed in a pan with apropeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 3603, and the Modaflow are introduced into the pan andmixed for 5 minutes at a speed of 5000 rpm. In the next step, the EGEDsilver powder and the Silver Flake #1 are introduced into the pan andare mixed for 1 to 2 minutes at a speed of 1000 rpm. Finally, the mixingspeed is increased to 10,000 rpm and mixed for an additional 5 to 10minutes.

Non-Urethane Containing Silver Composition for Producing Resistive Links

In accordance with another aspect of the invention, a presentlypreferred photocurable silver composition (“silver composition”) isprovided. This composition upon photocuring produces a coating capableof producing resistive links in circuit boards. In this preferredembodiment, the silver composition includes an acrylated epoxy oligomer.The acrylated epoxy oligomer is present in an amount of about 16% to20%, and preferably about 18%, of the silver composition. Suitableacrylated epoxy oligomers are the same as listed above. The preferredacrylated epoxy oligomer is Ebecryl 3603, which tri-functional acrylatedepoxy novolac. Combinations of these materials may also be employedherein.

The preferred silver composition also includes an isobornyl acrylatemonomer in an amount of about 8% to 14%, and preferably about 11%, ofthe silver composition. Suitable isobornyl acrylate monomers are thesame as listed above. Preferred isobornyl acrylate monomers includeSartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA AND IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing. Combinations of these materials may also be employedherein.

This preferred silver composition also includes a photoinitiator in anamount of about 4% to 8%, and preferably about 6%, of the silvercomposition. Suitable photoinitiators are the same as those listedabove. The preferred photoinitiator is Irgacure 1700 commerciallyavailable from Ciba-Geigy of Tarrytown, N.Y. Combinations of thesematerials may also be employed herein.

The preferred silver composition still further includes a flow promotingagent in an amount of about 0.1% to 2%, and preferably about 1.0%, ofthe silver composition. Suitable flow promoting agents are the same asthose listed above. The preferred flow promoting agent is Modaflow whichis an ethyl acrylate and 2-ethylhexyl acrylate copolymer that improvesthe flow of the composition. Combinations of these materials may also beemployed herein.

The preferred silver composition also includes a silver powder in anamount of about 25% to 35%, and preferably about 30%, of the silvercomposition. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

The preferred silver composition further includes a silver flakecomposition in an amount of about 25% to 38%, and preferably about 34%,of the silver composition. The preferred silver flake compositions areSilver Flake #25, Silver Flake #1, and Silver Flake #7A commerciallyavailable from Degussa Corp. of South Plainfield, N.J.

To illustrate, the following example sets forth a presently preferredsilver composition according to this aspect of the invention.

EXAMPLE 5

This example provides another preferred silver composition according tothe invention that when applied to a surface and subsequently cured byultraviolet radiation will produce a coating suitable for makingresistive links on circuit board. The silver composition was made fromthe following components:

Component Approximate Mass % Ebecryl 3603 18.3 IBOA 11.1 Silver PowderEGED 30.0 Silver Flake #1 33.5 Irgacure 1700  6.1 Modaflow  1.0 Total100.00

In this example the IBOA and Iragure 1700 are mixed in a pan with apropeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 3603 and the Modaflow are introduced into the pan andmixed for 5 minutes at a speed of 5000 rpm. In the next step, the EGEDsilver powder and the Silver Flake #1 are introduced into the pan andare mixed for 1 to 2 minutes at a speed of 1000 rpm. Finally, the mixingspeed is increased to 10,000 rpm and mixed for an additional 5 to 10minutes.

Urethane Containing Silver Composition for Producing Resistive Links

In accordance with one aspect of the invention, a presently preferredphotocurable silver composition (“silver composition”) is provided. Thiscomposition upon photocuring produces a coating capable of producingresistive links in circuit boards. In this preferred embodiment, thesilver composition includes an aliphatic acrylated oligomer. Thealiphatic acrylated oligomer is present in an amount of about 7% to 11%,and preferably about 9%, of the silver composition. The aliphaticacrylated oligomer preferably comprises a urethane oligomer. Suitablealiphatic acrylated oligomers are the same as those listed above. Thepreferred aliphatic acrylated oligomers include Ebecryl 264 and Ebecryl284. Ebecryl 264 is an aliphatic urethane triacrylate supplied as an 85%solution in hexandiol diacrylate. Ebecryl 284 is aliphatic urethanediacrylate of 1200 molecular weight diluted with 1,6-hexandioldiacrylate. Combinations of these materials may also be employed herein.

This preferred silver composition further includes an acrylated epoxyoligomer. The acrylated epoxy oligomer is present in an amount of about1% to 4%, and preferably about 3%, of the silver composition. Suitableacrylated epoxy oligomers are the same as those listed above. Thepreferred acrylated epoxy oligomer is Ebecryl 3603, which tri-functionalacrylated epoxy novolac. Combinations of these materials may also beemployed herein.

The preferred silver composition also includes an isobornyl acrylatemonomer in an amount of about 12% to 25%, and preferably about 22%, ofthe silver composition. Preferred isobornyl acrylate monomers includeSartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA and IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing. Combinations of these materials may also be employedherein.

This preferred silver composition also includes a photoinitiator in anamount of about 2% to 4%, and preferably about 3%, of the silvercomposition. Suitable photoinitiators are the same as those listedabove. The preferred photoinitiator is Irgacure 1700 commerciallyavailable from Ciba-Geigy of Tarrytown, N.Y.

The preferred silver composition further includes a antimony tin oxidepowder in an amount of 7% to 19%, and preferable about 17% of the silvercomposition. The preferred antimony tin oxide powder in Minatec 40commercially available from EM Industries of Hawthorne, N.Y.

The preferred silver composition still further includes a flow promotingagent in an amount of about 0.0% to 4%, and preferably about 2.0%, ofthe silver composition. Suitable flow promoting agents are the same asthose listed above. The preferred flow promoting agent is Modaflow whichis an ethyl acrylate and 2-ethylhexyl acrylate copolymer that improvesthe flow of the composition.

The preferred silver composition also includes a silver powder in anamount of about 24% to 30%, and preferably about 27%, of the silvercomposition. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

The preferred silver composition further includes a silver flakecomposition in an amount of about 15% to 30%, and preferably about 17%,of the silver composition. The preferred silver flake compositions areSilver Flake #25, Silver Flake #1, and Silver Flake #7A commerciallyavailable from Degussa Corp. of South Plainfield, N.J.

EXAMPLE 6

This example provides another preferred silver composition according tothe invention that when applied to a surface and subsequently cured byultraviolet radiation will produce a coating suitable for makingresistive links on circuit board. The silver composition was made fromthe following components:

Component Approximate Mass % Ebecryl 264  8.7 Ebecryl 3603  2.9 IBOA22.4 Silver Flake # 7A 17.0 Silver powder CED 26.5 Minatec 40 17.2Iragure 1700  3.3 Modaflow  2.0 Total 100.00

In this example the IBOA and Iragure 1700 are mixed in a pan with apropeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the CED silver powder, the Minatec 40, and the Silver Flake#7A are introduced into the pan and are mixed for 1 to 2 minutes at aspeed of 1000 rpm. Finally, the mixing speed is increased to 10,000 rpmand mixed for an additional 5 minutes.

EXAMPLE 7

This example provides another preferred silver composition according tothe invention that when applied to a surface and subsequently cured byultraviolet radiation will produce a coating suitable for makingresistive links on circuit board. The silver composition was made fromthe following components:

Component Approximate Mass % Ebecryl 284 8.4 Ebecryl 3603 1.7 Ebecryl754 8.4 IBOA 15.7  Silver Powder CED 25.0  Silver Flake # 7A 28.5 Iragure 1700 2.5 Minatec 40 9.8 Total 100.00 

In this example the IBOA and Iragure 1700 are mixed in a pan with apropeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 754, Ebecryl 284, the Ebecryl 3603, and the Modafloware introduced into the pan and mixed for 1 to 2 minutes at a speed of1000 rpm. In the next step, the CED silver powder, and the Silver Flake#7A are introduced into the pan and are mixed for 1 to 2 minutes at aspeed of 1000 rpm. Finally, the mixing speed is increased to 10,000 rpmand mixed for an additional 5 minutes.

This example contains Ebecryl 754 as an additive. Ebecryl 754 is apolyacrylic oligomer/acrylate monomer blend commercially available fromRadcure UCB Corp. of Smyrna, Ga.

Black Colored Silver Composition for Producing Resistive Links

In accordance with one aspect of the invention, a presently preferredphotocurable silver composition (“silver composition”) is provided. Thiscomposition upon photocuring produces a dark-colored coating capable ofproducing resistive links in circuit boards. In this preferredembodiment, the silver composition includes an aliphatic acrylatedoligomer. The aliphatic acrylated oligomer is present in an amount ofabout 7% to 11%, and preferably about 9%, of the silver composition. Thealiphatic acrylated oligomer preferably comprises a urethane oligomer.Suitable aliphatic acrylated oligomers are the same as those listedabove. The preferred aliphatic acrylated oligomers include Ebecryl 264and Ebecryl 284. Ebecryl 264 is an aliphatic urethane triacrylatesupplied as an 85% solution in hexandiol diacrylate. Ebecryl 284 isaliphatic urethane diacrylate of 1200 molecular weight diluted with1,6-hexandiol diacrylate. Combinations of these materials may also beemployed herein.

This preferred silver composition further includes an acrylated epoxyoligomer. The acrylated epoxy oligomer is present in an amount of about2% to 4%, and preferably about 3%, of the silver composition. Suitableacrylated epoxy oligomers are the same as those listed above. Thepreferred acrylated epoxy oligomer is Ebecryl 3603, which tri-functionalacrylated epoxy novolac.

The preferred silver composition also includes an isobornyl acrylatemonomer in an amount of about 10% to 14%, and preferably about 12%, ofthe silver composition. Preferred isobornyl acrylate monomers includeSartomer SR423 IBOMA and SR506 IBOA; Radcure IBOA, commerciallyavailable from Radcure Corp.; IBOA AND IBOMA, commercially availablefrom CPS Chemical; and Genomer 1121, commercially available from RahnRadiation Curing.

This preferred silver composition also includes a photoinitiator in anamount of about 13% to 15%, and preferably about 14%, of the silvercomposition. The preferred photoinitiator is Irgacure 1700 commerciallyavailable from Ciba-Geigy of Tarrytown, N.Y.

The preferred silver composition further includes a carbon black powderin an amount of 5% to 12%, and preferable about 7% of the silvercomposition. The preferred carbon black powder is Printex L commerciallyavailable from EM Industries of Hawthorne, N.Y.

The preferred silver composition further includes a wetting agent in anamount of 0.5% to 3%, and preferable about 1.5% of the silvercomposition. The preferred wetting agent is BYK 207 L commerciallyavailable from Byk-Chemie of Wallingford, Conn.

The preferred silver composition still further includes a flow promotingagent in an amount of about 0.1% to 2%, and preferably about 1.0%, ofthe silver composition. The preferred flow promoting agent is Modaflowwhich is an ethyl acrylate and 2-ethylhexyl acrylate copolymer thatimproves the flow of the composition. It is obvious to one skilled inthe art that combinations of these materials may also be employedherein.

The preferred silver composition also includes a silver powder in anamount of about 30% to 40%, and preferably about 36%, of the silvercomposition. The preferred silver powders are Silver Powder EG-ED andSilver Powder C-ED commercially available from Degussa Corp. of SouthPlainfield, N.J.

The preferred silver composition further includes a silver flakecomposition in an amount of about 15% to 25%, and preferably about 18%,of the silver composition. The preferred silver flake compositions areSilver Flake #25, Silver Flake #1, and Silver Flake #7A commerciallyavailable from Degussa Corp. of South Plainfield, N.J.

EXAMPLE 8

This example provides another preferred silver composition according tothe invention that when applied to a surface and subsequently cured byultraviolet radiation will produce a coating suitable for making blackcolored resistive links on circuit board. The silver composition wasmade from the following components:

Component Approximate Mass % Ebecryl 264 8.8 Ebecryl 3603 2.5 Printex L7.3 Byk 207 1.5 IBOA 11.6  Silver Powder EGED 35.7  Silver Flake # 2518.4  Iragure 1700 13.5  Modaflow 0.7 Total 100.00 

In this example the IBOA and Iragure 1700 are mixed in a pan with apropeller blade mixer for 30 seconds at a speed of 500 to 1000 rpm.Next, the Ebecryl 264, the Ebecryl 3603, and the Modaflow are introducedinto the pan and mixed for 1 to 2 minutes at a speed of 1000 rpm. In thenext step, the EGED silver powder, the Silver Flake #25, and the PrintexL are introduced into the pan and are mixed for 1 to 2 minutes at aspeed of 1000 rpm. Finally, the BYK 207 in introduced and mixed for 5minutes at a speed of 10,000 rpm.

In describing each of the components in these examples and in thisdescription, the compositions have been described as “comprising” thestated component. Preferably each of those components consistsessentially of, and more preferably they consist exclusively of, thestated components, and from the stated sources.

The silver-containing composition as described above is referred to asbeing a “fluid phase” composition. This is meant to indicate that thecomposition is flowable as is a liquid, but is not otherwise limiting.Preferably, the silver composition comprises a liquid. The composition,for example, generally will be a slurry, in which the silver metalgrains (powder and flakes) are solid-phase particles suspended in theliquid phase or phases of the urethane, epoxy, and any other liquid oressentially liquid components.

Method for Preparing Silver Composition

In accordance with another aspect of the invention, a method is providedfor making a photocurable silver composition. In accordance with apreferred version, the method includes a first step of combining andmixing an isobornyl acrylate monomer and a photoinitiators to create afirst mixture. The isobornyl acrylate monomer is present in an amount ofabout 4% to 8% of the silver composition, and the photoinitiator ispresent in an amount of about 4% to 6% of the silver composition.

This preferred method preferably but optionally is carried out using amixing vessel of appropriate size, depending upon the desired batchsize. A glass or steel lined batch processing vessel of known design andcommercial availability typically will suffice.

This first step of the preferred method is carried out by placing thecomponents into the vessel while stirring, e.g., by a suitable impeller.

The method includes a second step of combining and mixing an aliphaticacrylated oligomer and an acrylated epoxy oligomer to create a secondmixture. The aliphatic acrylated oligomer is present in an amount ofabout 3% to 8% of the silver composition and the acrylated epoxyoligomer is present in an amount of about 2% to 4% of the silvercomposition. In accordance with this preferred method, this second stepis carried out sequentially after the first step, and involves blendingin these components into the first mixture, i.e., from the first step.

The method further includes a third step of combining and mixing asilver powder and a silver flake composition to create a third mixture.The silver powder is present in an amount of about 50% to 60% of thesilver composition and the silver flake composition is present An amountof about 25% to 35% of the silver composition. This step also preferablyis carried out in the vessel, preferably sequentially after completionof the second step.

The method further includes a fourth step of combining and mixing a flowpromoting agent in an amount of about 0.1% to 2% of the silvercomposition, and a fifth step of combining the first, second, third andfourth mixtures to create the silver composition.

These steps also preferably would be performed sequentially by addingthe cited components into the vessel while mixing with the impeller.

As noted, preferably but optionally, the first, second, third and fourthsteps are performed sequentially. This is not, however, limiting.Different processing orders may be used in accordance with the method.

Also as noted, the method in its various forms may be carried out on abatch basis, for example, in a mixing vessel or similar processequipment suitable for batch processing. It may also be carried out inother forms, for example, such as continuous flow regimes, e.g., usingknown continuous flow processing equipment and configurations for mixingthese components, preferably but optionally in the sequential orderidentified above.

In accordance with another aspect of the invention, another method isprovided for making an ultraviolet curable silver composition. Thismethod comprises a first step of combining and mixing an isobornylacrylate monomer and a photoinitiator to create a first composition,wherein the isobornyl acrylate monomer is present in an amount of about4% to 8% of the silver composition, and the photoinitiator is present inan amount of about 3% to 6% of the silver composition. This method alsoincludes a second step of combining with the first composition andmixing an aliphatic acrylated oligomer and an acrylated epoxy oligomerto create a second mixture. The aliphatic acrylated oligomer is presentin an amount of about 3% to 8% of the silver composition and theacrylated epoxy oligomer is present in an amount of about 2% to 4% ofthe silver composition.

The method further includes a third step of combining with the secondcomposition and mixing a silver powder and a silver flake composition tocreate a third composition. The silver powder is present in an amount ofabout 50% to 60% of the silver composition and the silver flakecomposition is present in an amount of about 25% to 35% of the silvercomposition.

The method still further includes a fourth step of combining with thethird composition and mixing a flow promoting agent in an amount ofabout 0.1% to 2% of the silver composition.

According to another aspect of the invention, a method is provided forpreparing a liquid-phase silver-containing composition for use inproviding a silver-containing coating, plating, film or layer on asubstrate. The presently-preferred version of the method includespreparing either of the preferred silver compositions as identified inthe examples above. The preferred version of this method includes afirst step of combining and mixing the monomer and the photoinitiator ina mixing vessel. The method includes a second step of adding to themixing vessel and blending into the previously-added components theurethane and the epoxy. The method also includes a third step of addingto the mixing vessel and blending into the components therein the silverpowder and the silver flake. The preferred method further includes afourth step of adding to the mixing vessel and blending into itspreviously-added components the flow agent.

Method for Depositing a Silver Coating on a Substrate

In accordance with still another aspect of the invention, a method isprovided for depositing a silver coating on a substrate. The methodcomprises a first step of applying a silver-containing fluid-phasecomposition (“silver composition”) to the substrate. Each of the silvercompositions described above are suitable for application to thesubstrate.

In a preferred embodiment, the silver composition that is applied to thesubstrate comprises an aliphatic acrylated oligomer, the aliphaticacrylated oligomer being present in an amount of about 3% to 8% of thesilver composition; an acrylated epoxy oligomer, the acrylated epoxyoligomer being present in an amount of about 2% to 4% of the silvercomposition; an isobornyl acrylate monomer in an amount of about 4% to8% of the silver composition; a photoinitiator in an amount of about 3%to 6% of the silver composition; a flow promoting agent in an amount ofabout 0.1% to 2% of the silver composition; a silver powder in an amountof about 50% to 60% of the silver composition; and a silver flakecomposition in an amount of about 25% to 35% of the silver composition.The preferred silver compositions according to this method are thosedescribed herein, for example, including the compositions described inthe examples.

The silver composition may be applied to the substrate using a number ofdifferent techniques. The silver composition may be applied, forexample, by direct brush application, or it may be sprayed onto thesubstrate surface. It also may be applied using a screen printingtechnique. In such screen printing technique, a “screen” as the term isused in the screen printing industry is used to regulate the flow ofliquid composition onto the substrate surface. The silver compositiontypically would be applied to the screen as the latter contacts thesubstrate. The silver composition flows through the silk screen to thesubstrate, whereupon it adheres to the substrate An the desired filmthickness. Screen printing techniques suitable for this purpose includeknown techniques, but wherein the process is adjusted in ways known topersons of ordinary skill in the art to accommodate the viscosity,flowability, and other properties of the liquid-phase composition, thesubstrate and its surface properties, etc. Flexographic techniques, forexample, using pinch rollers to contact the silver composition with arolling substrate, also may be used.

The method includes a second step of illuminating the silver-containingfluid-phase composition on the substrate with an ultraviolet light tocause the silver-containing fluid-phase composition to cure into thesilver coating. This illumination may be carried out in any number ofways, provided the ultraviolet light or radiation impinges upon thesilver composition so that the silver composition is caused topolymerize to form the coating, layer, film, etc., and thereby cures.Such formed layers have a resistivity from 0.03 to 0.50 ohms/sq at 1mil.

Curing preferably takes place by free radical polymerization, which isinitiated by an ultraviolet radiation source. The photoinitiatorpreferably comprises a photoinitiator, as described above.

Various ultraviolet light sources may be used, depending on theapplication. Preferred ultraviolet radiation sources for a number ofapplications include known ultraviolet lighting equipment with energyintensity settings of, for example, 125 watts, 200 watts, and 300 wattsper square inch.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrative examples shown and described. Accordingly, departures maybe made from such details without departing from the spirit or scope ofthe general inventive concept.

What is claimed is:
 1. A method for depositing a silver coating on asubstrate, the method comprising: a first step of applying to thesubstrate a composition comprising: an aliphatic acrylated urethaneoligomer; an acrylated epoxy oligomer; an isobornyl acrylate monomer; aphotoinitiator; silver powder; and silver flakes in an amount of atleast 20% relative to the weight of the silver powder; and a second stepof photocuring by exposure to light of a wavelength effective to curesaid composition.
 2. A method as recited in claim 1, wherein the firststep comprises spraying the silver-containing fluid-phase compositiononto the substrate.
 3. A method as recited in claim 1, wherein the firststep comprises applying the silver-containing fluid-phase composition tothe substrate using a screen printing technique.
 4. A method as recitedin claim 1, wherein the first step comprises applying thesilver-containing fluid-phase composition to the substrate using aflexographic technique.
 5. A photocurable silver composition consistingessentially of: a photocurable organic mixture; a photoinitiator; silverpowder; and silver flakes in an amount of at least 20% relative to theweight of the silver powder, wherein the photocurable organic mixturecomprises an aliphatic acrylated urethane oligomer and the photocurablesilver composition when illuminated with ultraviolet (UV) light curesinto a silver coating.
 6. The silver composition recited in claim 5wherein the aliphatic acrylated urethane oligomer is present in anamount of about 3% to 8% of the silver composition.
 7. The silvercomposition recited in claim 5 wherein the aliphatic acrylated urethaneoligomer is present in an amount of about 8% of the silver composition.8. The photocurable silver composition of claim 5 wherein thephotocurable organic mixture further comprises an acrylated epoxyoligomer.
 9. The silver composition recited in claim 8 wherein theacrylated epoxy oligomer is present in an amount of about 2% to 4% ofthe silver composition.
 10. The silver composition recited in claim 8wherein the acrylated epoxy oligomer is present in an amount of about 3%of the silver composition.
 11. The photocurable silver composition ofclaim 8 wherein the photocurable organic mixture further comprises anisobornyl acrylate monomer.
 12. The silver composition recited in claim11 wherein the isobornyl acrylate monomer is present in an amount ofabout 4% to 8% of the silver composition.
 13. The silver compositionrecited in claim 11 wherein the isobornyl acrylate monomer is present inan amount of about 5% of the silver composition.
 14. The silvercomposition recited in claim 11 wherein the photocurable organic mixturefurther comprises a flow promoting agent.
 15. The silver compositionrecited in claim 14 wherein the flow agent is present in an amount ofabout 0.1% to 2% of the silver composition.
 16. The silver compositionrecited in claim 14 wherein the flow agent is present in an amount ofabout 1% of the silver composition.
 17. The silver composition recitedin claim 5 wherein the silver powder is present in an amount of about50% to 60% of the silver composition.
 18. A silver composition asrecited in claim 5 wherein the silver powder is present in an amount ofabout 52% of the silver composition.
 19. The silver composition asrecited in claim 5 wherein the silver flakes are present in an amount ofabout 25% to 35% of the silver composition.
 20. The silver compositionrecited in claim 5 wherein the silver flakes is present in an amount ofabout 30% of the silver composition.
 21. The silver composition recitedin claim 5 wherein the photoinitiator is present in an amount of about3% to 6% of the silver composition.
 22. The silver composition recitedin claim 5 wherein the photoinitiator is present in an amount of about5% of the silver composition.